By stepping down immediately, Cantor enables the current Republican caucus to elect his successor. If he were to serve through the remainder of this Congress, then the new caucus with many more Conservative would select the Majority Leader. Of course, there will be a new election within the new caucus in January, but they are much less likely to throw out an incumbent. See how politics works?
Thanks for putting it in perspective. I was wondering why he would step down early.
On the positive side, if their choice screams business as usual, it increases the odds of a revolt next January where Bonehead gets tossed.